Los Angeles is known not only for its celebrity clientele, but also for its congested roadways and heavy traffic, which consequently has led to severely polluted air, and the title of the "smoggiest city" in the United States. While air quality has improved somewhat in LA, a joint study by UCLA and the California Air Resources Board suggests that nearly a quarter of Angelenos are exposed to noxious plumes of freeway fumes almost every morning, far more people than previously thought.

ADVERTISEMENT

Researchers found that overnight atmospheric conditions concentrate freeway pollutants in a plume stretching 1.5 kilometers (approximately 0.93 miles) downwind. These pollutants can seep inside homes and buildings, and lingering as late as 10 a.m. Although closed windows can help block particles from entering homes, previous studies have shown that indoor pollution levels still reach 50 to 70 percent of outdoor levels, the researchers noted.

This study shows that the same effect would be expected downwind of any highway nationwide, the researchers said.

The 1.5 kilometer measurement is in striking contrast to earlier studies in the United States and Australia showing that daytime pollutant concentrations extended no more than about 300 meters (about 0.19 mile) downwind of major roadways, and confirms an earlier UCLA study that showed the same result at a single coastal location.

The research team measured pollutant concentrations upwind and downwind of four major LA freeways using a zero-emission vehicle equipped with specialized instruments to quantify the amount of ultrafine particles and other tailpipe pollutants such as nitrogen oxide and carbon monoxide. Researchers drove down streets perpendicular to the freeways and recorded the pollutant levels.

"This is happening around every freeway," said Professor Suzanne Paulson of UCLA's Department of Atmospheric and Oceanic Sciences and the Institute of the Environment and Sustainability, who headed the study. "It's clear that heavily trafficked roadways have a large impact on downwind populations, and a similar situation likely happens around the world in the early morning hours. The particles tend to end up indoors, so a lot of people are being exposed inside their homes and schools."

Freeway pollutants have been linked to many health issues including increases in asthma, heart attacks, strokes, and low birth weigh. To limit your exposure to this air, avoid outdoor early morning recreational activities near these freeways and close your windows during early morning hours.